JPS6072307A - Amplitude limiting circuit - Google Patents

Abstract

PURPOSE:To make excellent transmission in a desired band width, by installing an amplitude limiting circuit having two diodes which are at least push-pull connected with the input-output terminal of a feedback type oscillating circuit and a capacitor which is connected in series with the diodes. CONSTITUTION:A capacitor C7 for cutting DC and feedback diodes D1 and D2 are added to a feedback type Colpitts oscillating circuit. The capacitor C7 is connected in series with the push-pull connection of the diodes D1 and D2 and the serial circuit is inserted between the collector and base of an oscillating transistor T so that the serial circuit is connected in parallel with a serial resonance circuit composed of an inductance L and capacitor C3. Therefore, the frequency-amplitude characteristic of the amplitude limiting circuit of this invention is lowered from the characteristic A shown by the dotted line to the characteristic B shown by the solid line. As a result, an outputted high frequency signal is limited in amplitude and becomes a high frequency signal having a stable constant amplitude, and thus, an excellent transfer characteristic is obtained.

Description

[Detailed Description of the Invention] [Technical Part of the Invention mf] This invention relates to a width limiting circuit, particularly an injection-locked oscillation circuit used in FM receivers such as SHF receivers, so-called ILO (Injection Locked O8C).
, ) configuration of an amplitude limiting circuit.

[Technical background of the invention]

Generally, an FM receiver first converts an FM wave signal into an amplitude modulated wave, and then detects and demodulates the wave. In this case, a change in the amplitude of the input FM wave signal directly becomes a change in the demodulated output. Therefore, when a noise signal is added to the FM wave signal, the amplitude change due to the noise signal appears in the output, so that the degree of improvement in noise performance by the XFM method cannot be achieved at all.

For this reason, in actual demodulation, an amplitude limiting circuit is provided.
After the amplitude of the FM wave signal is limited by this amplitude limiting circuit, it is demodulated by, for example, a frequency discriminator. By the way, as an amplitude limiting circuit for high frequency signals,
In general, amplitude limiting circuits that fully utilize the nonlinearity of diodes,
There is a so-called diode limiter.

However, this diode limiter has the disadvantage that a sufficient amplitude limiting effect cannot be obtained unless the input amplitude of the high frequency signal is made large, and also has the disadvantage that the high frequency signal is significantly attenuated.

Therefore, in recent years, amplitude limiting circuits having an ILO configuration are often used. Compared to the above-mentioned diode limiter, this ILO-configured amplitude limiting circuit can be a single sufficient amplitude limiting circuit even if the input amplitude of the high-frequency signal is small.

FIG. 1 is a circuit diagram showing a conventionally used amplitude limiting circuit having an ILO configuration. In the figure, oscillation transistor T, resistor R1+ R2+ R3rRl, capacitor C1
constitutes an amplifier circuit.

In this case, the resistors R1+R2+Rs+R4 provide a bias to the oscillation transistor T. Also,:'
The emitter of the oscillation transistor T of the sensor C4 is grounded for all AC currents. A Colpitts oscillation circuit 1 is formed by connecting capacitors C1+C2r 03 and inductance Lf to such an amplifier circuit, and completely oscillates freely. The high frequency signal is injected from the input terminal 1N to the base of the oscillation transistor T via the capacitor Csk. Then, the output high frequency signal faithfully locked to the input high frequency signal is guided to the output terminal OUT K through the capacitor c6. Note that +B is a power supply.

[Problems with background technology]

However, in the case of the configuration shown in FIG. 1, there are problems such as a complicated circuit configuration, which will be explained below.

In the configuration shown in Figure 1, in the frequency range in which the output high-frequency signal is locked to the input high-frequency signal (hereinafter referred to as the lock range), the amplitude of the output high-frequency signal is constant regardless of the frequency of the input high-frequency signal. Generally, when the amplitude of the input high-frequency signal is large, the lock range R becomes wider, as shown by the characteristic curve A in FIG. 2, but the transfer characteristics deteriorate. Furthermore, when the amplitude of the input high-frequency signal is small, the lock range RB is narrow and the transfer characteristic becomes unimodal, as shown in characteristic trend 11iIB.

Therefore, if the amplitude limiting circuit configured as shown in FIG.
When used in a system that handles signals with a wide bandwidth, such as an F receiver, it is necessary to take all measures to deal with the deterioration of transfer characteristics due to the expansion of the lock range. If this treatment is not fully carried out, the differential gain and differential phase of the demodulated signal will deteriorate, resulting in deterioration of image quality.

For this reason, conventionally, when inputting all high-frequency signals to an amplitude limiting circuit with an ILO configuration, for example, the entire amplitude of the input high-frequency signal is determined with priority given to obtaining the desired lock range, and the amplitude limiting circuit with an ILO configuration By limiting the amplitude of the output high frequency signal using another amplitude limiting circuit such as a diode limiter, the transfer characteristics are fully compensated. In addition,
When a high frequency signal is input to an amplitude II@limiting circuit having an ILO configuration, the high frequency signal is generally input after being set to a predetermined constant amplitude in all stages of the automatic gain control amplifier circuit.

In this way, conventionally, a single amplitude limiting circuit with an ILO configuration can handle S
The problem is that the amplitude limiting operation in an HF receiver cannot be satisfied, and a compensation circuit for improving transfer characteristics is required, resulting in a complicated circuit configuration. Furthermore, the conventional configuration has the problem that it is extremely difficult to achieve both optimization of the amplitude limiting effect and optimization of the transfer characteristic.

[Purpose of the invention]

It is an object of the present invention to provide an amplitude limiting circuit which can easily obtain good transfer characteristics at a desired bandwidth.

[Summary of the invention]

The present invention provides an amplitude limiting means having at least two diodes that are coupled in a butshull manner and a capacitor connected in series with the two diodes that are coupled in series with respect to the input and output terminals of a feedback oscillation means such as a Colpitts oscillation circuit. It is configured to insert all the parts.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 3 is a circuit diagram of one embodiment. In FIG. 3, the same parts as in FIG. 1 are given the same reference numerals. The difference between FIG. 3 and FIG. 1 is that a DC cut capacitor C7 and feedback diodes D, D2 are added to the Colpitts oscillation circuit as feedback oscillation means.

That is, the diode D1. D, is push-sol coupled, and capacitor C7 is connected to this diode D 1 ,
+ 'D 2 is connected in series to the push-pull coupling. This series circuit is inserted between the collector and paste of the oscillation transistor T so as to be parallel to the series resonant circuit as a tuning circuit consisting of the inductance L and capacitor C3. Diode D,,'D.

is, for example, a Schottky barrier f-) type diode.

The push-pull coupled diode D1. D.

The feedback circuit functions to reduce the amplitude of the oscillation output high frequency signal of the amplitude limiting circuit from point 11A to solid line B, as shown in FIG. The nonlinear behavior of diodes is well known and exhibits almost the same characteristics regardless of frequency.

Therefore, the output high frequency signal shown by the characteristic curve B is sufficiently limited in amplitude, becomes a stable high frequency signal with a constant amplitude, and good transfer characteristics are obtained.

In addition, since the amplitude of the high-frequency signal is limited by the feedback circuit formed by the bush-glue coupling of the diodes D, D, the lock range fB is greatly expanded compared to the lock range f^ without the feedback circuit. Even if the total input amplitude of the high frequency signal is reduced, a sufficient lock range can be ensured. Additionally, by being able to reduce the input amplitude of the high-frequency signal in this way, it is possible to avoid as much as possible deterioration of the transfer characteristics due to an increase in the input amplitude.
Coupled with the amplitude limiting effect of the +Ii feedback circuit (of A-do IJ, b), the transfer characteristics can be further improved.

Here, the free oscillation frequencies of the Colpitts oscillation circuit and the amplitude limiting circuit of FIG. 3 will be explained using FIGS. 5 and 6.

In the Colpitts oscillation circuit shown in FIG. 5, T is an oscillation transistor, Cl1C1 is an oscillation capacitor, and L is an oscillation inductance.

Fig. 6 is an equivalent circuit of Fig. 6, and in the same figure, T is an oscillation transistor, Cl102 is an oscillation capacitor,
L is an oscillation inductance.

Further, Cs is a capacitor for completely stabilizing the oscillation frequency. CD is a diode D1. This is the capacitance between the terminals of D2. Capacitor C2 is a large capacitor that is unrelated to oscillation.

Generally, the diode D1. The capacitance C between the terminals of D
D is affected by reverse bias voltage.

In the amplitude limiting circuit shown in Fig. 3, two diodes D,
Because of Dzk bush-sol coupling, a reverse voltage is applied to the off-state diode during a period when one diode is on and the other is off. If the total inter-terminal capacitance at this time is CD as shown in Figure 6, then
Oscillation inductance L1 stabilizing capacitor Cat”
The included equivalent inductance L' is rounded.

Here, if the series capacitance of the capacitor cx+Cz in the general Colpitts oscillation circuit shown in Fig. 5 is set to M, then
The oscillation frequency ω0 is as follows. Here, if we replace the oscillation inductance L with the equivalent inductance L', we get the following.

In this way, the amplitude limiting circuit shown in FIG. 3 is the same as the Colpitts oscillation circuit shown in FIG. 6.

Note that the inter-terminal capacitance CD of the diodes D, D2 is extremely small compared to the capacitance of the oscillation capacitors C1 and C2. It has been confirmed through experiments that it is not affected by the capacitance CO.According to this embodiment detailed above, the amplitude of the high frequency signal is sufficiently controlled by the feedback circuit formed by the diode Dr + D2 in the amplitude limiting circuit. Because the full amplitude limiting effect is achieved,
Its transfer characteristics can be totally improved. Moreover, this eliminates the problem of optimizing the amplitude limiting effect and optimizing the transfer characteristic at the same time when determining the human force amplitude of the high-frequency signal, thereby facilitating circuit design.

Further, since the lock range is widened by the amplitude limiting action of the feedback circuit, a desired lock range can be obtained even if the input amplitude of the high frequency signal is small. And input amplitude 7
By making it smaller, deterioration of the transfer characteristics can be suppressed as much as possible, and in combination with the improvement of the transfer characteristics due to the amplitude limiting action of the feedback circuit, it is possible to further improve the transfer characteristics.

Also, high frequency signals? By being able to reduce the total input amplitude, the main body of the amplitude limiting circuit excluding the feedback circuit described above,
In other words, the lock range of the Colpitts oscillator circuit can be narrowed, and it can be used as a tracking filter for all kinds of circuits.

This makes it possible to improve the threshold phenomenon peculiar to 1M transmission.

FIG. 7 is a circuit diagram showing another embodiment of the present invention. In FIG. 7, the same parts as in the previous FIG. 3 are all designated by the same reference numerals.

In this embodiment, a resistor R6 having a small resistance value of about iooΩ is inserted in the amplitude limiting means consisting of feedback diodes D□, D2 and capacitor C7 so as to be connected in series with the feedback diodes D□, D2 and capacitor C2. It is. By doing so, the amount of feedback can be adjusted according to the resistance value of the resistor R6, and the output level and lock range can be finely adjusted.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an amplitude limiting circuit that can easily obtain good transfer characteristics in a desired bandwidth.

[Brief explanation of the drawings] Figure 1 is a circuit diagram showing the inside of a conventional amplitude limiting circuit, and Figure 2 is a diagram showing the relationship between the frequency and output amplitude of a high-frequency signal to explain the entire operation of the circuit shown in Figure 1. 3 is a circuit diagram showing an embodiment of the amplitude limiting circuit according to the present invention, and FIG. 4 shows the frequency and output amplitude of a high-frequency signal shown to explain the operation of the circuit shown in FIG. Figure 5 is an equivalent circuit diagram of the Colpitts oscillation circuit shown to compare the operation of the circuit shown in Figure 3 and the Colpitts oscillation circuit, and Figure 6 is the equivalent circuit diagram of the circuit shown in Figure 3. The circuit diagram and FIG. 7 are circuit diagrams showing all other embodiments of the present invention.
Terminal, 10B...power supply, R1-R6...resistance, T...
・Oscillation transistor, 01 to C7... Capacitor, D
l, D2...m M p' iode. Applicant's agent Patent attorney Takehiko Suzue No. 11″τ Figure 2 Figure 3!゛4 Figures 4 and 5 ・Figure 36

Claims (1)

[Claims] Feedback oscillation means comprising a tuning circuit inserted between output terminals of a high-frequency amplifier circuit, at least two diodes coupled in a push-pull manner and connected in series with the two diodes coupled in a push-pull manner. and amplitude limiting means inserted in parallel with the tuning circuit between the input and output terminals of the high frequency amplifier circuit.